1. The Field of the Invention
The present invention relates generally to surgical fasteners. More particularly, it concerns an implant for repairing meniscal tearing in the knee.
2. The Background Art
Intracorporeal tearing in body tissue occurs most often at bone joint regions. Certain body tissues act as a cushion for absorbing the forces of joint movement, preventing friction in the joint, and channeling the mechanical stress and strain associated with such movement. Like any shock-absorbing material, such body tissues experience failure when applied forces exceed the strength of the material, including failure in shear and tension.
Human joints include a type of shock-absorbing body tissue known as a "meniscus." Such body tissue comprises a fibrous cartilage. In each human knee there are two generally crescent-shaped menisci on opposite sides of the knee (see FIG. 1), referred to in the medical field as a medial meniscus and a lateral meniscus. Different types of tearing occur in the knee menisci, perhaps twenty percent of which are repairable by mechanical connecting apparatus. Most of these repairable tears occur in the outer two thirds of the knee meniscus, since the knee meniscus is generally triangular in cross section (see FIG. 2), tapering inwardly to a small inner edge that is sometimes not conducive to mechanical repair.
Untreated meniscal tearing may deteriorate and cause further complications. It is known in the surgical field to repair tears in the meniscus by holding the sides of the tear together, usually for at least six weeks, to allow the body to regenerate the tissue needed to hold the tear together.
Several different techniques have been developed for repairing meniscus tears. Many of the presently known techniques for repairing meniscal tearing in the knee have proven to be a significant benefit in the relief of knee injury, pain and discomfort. Four major techniques are known in the field of meniscus repair: "open" technique, "inside-out" technique, "outside-in" technique and "all inside" technique. These techniques generally involve suturing the sides of a meniscus tear together. Such techniques, while useful, are laborious to perform and sometimes fail to provide adequate holding strength during the healing period, since the sutures rely only upon fixation points on the exterior edges of the meniscus.
Attempts have been made to provide additional fixation points within the meniscus itself, to increase the holding strength of the repair. U.S. Pat. No. 4,873,976 (granted Oct. 17, 1989 to Schreiber) discloses a rigid implant that resembles a sharp-tipped tack, and has barbs along its length. The rigid implant is pressed into a torn meniscus to approximate the tear, and the barbs of the implant function as internal fixation points. U.S. Pat. No. 5,059,206 (granted Oct. 22, 1991 to Winters) discloses a similar tack-like meniscus repair implant, and a flexible-tipped delivery device for deploying the implant.
These prior art apparatus and methods, while useful, are nevertheless characterized by several disadvantages. The rigid implants of Schreiber and Winters appear to require a fixation point against the inner edge of the meniscus and fail to provide a fixation point against the outer edge. Further, their methods of deploying the implant are to force the implant and its sharp barbs directly into the tissue, causing the barbs to tear into the meniscus before coming to rest at the proper position, thereby risking a reduction in strength and fixation of the internal fixation points.